I'm trying to record voice from a microphone into my laptop. Unfortunately, the laptop does not have a microphone jack, so I have to use the USB input. This doesn't present a problem when I record voice from my gaming headset, but when I record from the condenser microphone over USB I get a very pronounced line hum. This occurs even when the laptop is unplugged from power and on its battery.
The hum consists mainly of 55 Hz noise, but with some 110 and 512 Hz components. I can eliminate this using a notch filter in "post production", as it were, but I'd rather not have to do this. This noise is not the fault of the microphone, by the way (at least not directly), since when I run the microphone signal into my digital voice recorder (using a 3.5mm plug) there is no background hum at all.
Is there some way to process or filter the output from the microphone so that this noise never makes it to the laptop?